Globally averaged land surface temperatures, 1900-2014 (GHCN)

Christopher Booker thinks NOAA is distorting global land temperature data to
inflate reported global warming, and fan the flames of climate alarmism, and he's
written a couple of articles about it.

Dr. Kevin Cowtan contends Booker is wrong, and he created a YouTube video about
it. Dr. Cowtan trusts that NOAA's adjustments are justified and correct, and he also
says they are too minor to be questionable.
“Why would they do that?” he asks at the end of his video, meaning
why would anyone commit fraud for an inconsequential difference in the result?

I don't know with certainty whether
or not NOAA's adjustments are all justified and correct, but I found Dr. Cowtan's argument
unpersuasive, for two reasons.

The first reason is that he's assuming that fraudulent intent is the only possible
explanation for biased results, but it isn't. If the results are biased to
exaggerate warming, it could also be due to
confirmation bias
or other error, even by
people with the best of intentions.

However, Dr. Cowtan's argument also depends on the adjustments being inconsequential,
and they are not. I digitized the endpoints of one of Dr. Cowtan's graphs using
WebPlotDigitizer and found that
his own analysis proves NOAA's adjustments are far from inconsequential. By comparing
the adjusted and unadjusted versions of Dr. Cowtan's graphs of globally averaged land
surface temperatures, I found that NOAA's adjustments increased the reported warming
by 35%.